The present invention relates to a suspension control apparatus to be mounted in a vehicle such as, for example, a four-wheeled automobile, which is suitably used for damping vibrations of the vehicle.
In general, a suspension control apparatus is mounted in a vehicle such as an automobile as described in, for example, Japanese Patent Application Laid-open No. 2003-11635. The suspension control apparatus described in Japanese Patent Application Laid-open No. 2003-11635 includes a damping-force adjusting type shock absorber provided between a vehicle-body side and each axle side. The suspension control apparatus is configured to variably control damping-force characteristics obtained by the shock absorber according to a vehicle attitude caused with a braking operation of a brake.
The suspension control apparatus described in Japanese Patent Application Laid-open No. 2003-11635 controls the damping-force adjusting type shock absorber so as to increase a wheel load of a braked wheel and reduce a wheel load of an non-braked wheel when an antiskid brake system (electronic stability control system) is actuated. According to the above-mentioned method, a braking force is increased by the damping-force adjusting type shock absorber so as to improve running stability. The following document “An Experimental Evaluation of G-Vectoring Vehicle Performance which Decelerates Automatically in Coordination with Lateral Motion” by Shinjiro Saito, Makoto Yamakado, Atsushi Yokoyama, Junya Takahashi, and Masato Abe, Transactions of Society of Automotive Engineers of Japan, May 2009, Volume 40, No. 3, pp. 629 to 634 (hereinafter, referred to as “Non-Patent Document 1”), discloses a configuration which controls an acceleration/deceleration of a vehicle according to a lateral motion of the vehicle to enhance the stability of the vehicle.
By the way, the suspension control apparatus described in Japanese Patent Application Laid-open No. 2003-11635 does not control the damping-force adjusting type shock absorber when the antiskid brake system is not actuated. Therefore, the potential of occurrence of an unstable running state of the vehicle remains the same. Specifically, even for the vehicle in which the suspension control apparatus described above is mounted, a limit value at which the running state of the vehicle becomes unstable to actuate the antiskid brake system is the same as that for a vehicle in which the suspension control apparatus is not mounted. Therefore, the suspension control apparatus described in Japanese Patent Application Laid-open No. 2003-11635 does not have the effects of reducing a likelihood of bringing about the unstable running state described above.
Moreover, in the suspension control apparatus described in Japanese Patent Application Laid-open No. 2003-11635, if a piston rod is in a fully-extended or fully-compressed state when, for example, the antiskid brake system is actuated, the damping force cannot be generated. Therefore, there is a problem in that the wheel loads cannot be controlled in such a state and hence, running stability cannot be improved.
On the other hand, Non-Patent Document 1 discloses the configuration for controlling the acceleration/deceleration of the vehicle according to the lateral motion of the vehicle so as to enhance the stability of the vehicle at cornering. However, the configuration described in Non-Patent Document 1 takes only deceleration control of the vehicle into main consideration and does not take the application to the suspension control apparatus into consideration.